This invention relates generally to microfluidic devices, and in particular, to a method of fabricating three-dimensional microstructures.
As is known, microfluidic devices are being used in an increasing number of applications. However, further expansion of the uses for such microfluidic devices has been limited due to the difficulty and expense of fabrication. In order to more efficiently fabricate these devices, various methods of manufacture have been borrowed from the integrated circuit industry. These methods have led to the development of two-dimensional or pseudo three-dimensional (orthogonal) microscale structures. Unfortunately, present methods to construct non-orthogonal shapes (smooth curves, etc.) at the microscale level are limited. Curved microstructures are highly desirable since such structures have different stress distributions upon mechanical loading than orthogonal structures. Further, microstructures having curved sidewalls allow for different flow patterns through the channels of a microfluidic device, as compared to orthogonal geometries, thereby providing more efficient mixing designs and more lifelike environments for biological studies.
Traditional methods of fabricating microelectromechanical systems (MEMS) involve the creation of three-dimensional structures by forming layers on top of one another or by etching a bulk substrate. The sidewalls of the individual layers of the structures can be vertical, angled or curved depending on the process used to create the layer. For example, vertical sidewalls can be formed in a layer by the rapid ion etching (RIE) of the layer. Angled sidewalls can be formed by chemically etching a layer along a crystal plane. Curved sidewalls can be created by the diffusion-limited chemical etching of a layer. Although a variety of sidewall shapes are possible with these prior methods, control over the shapes of the sidewall is limited by the angle of the crystal plane or the physics of the chemical or ion etch. Vertical structures can also be achieved by electroplating. However, microscale electroplating is relatively expensive, time consuming and difficult to control. Three-dimensional structures of arbitrary shape have been demonstrated with two-photon polymerization, but the process requires expensive equipment and is slow, as the geometry must be xe2x80x9cwrittenxe2x80x9d piece by piece. In view of the foregoing, it can be appreciated that a method of farbrication that allows for the rapid construction of smooth three-dimensional microstructure geometries would be a significant advancement in the art.
Therefore, it is a primary object and feature of the present invention to provide a method of fabricating a microstructure that is simple and inexpensive.
It is a further object and feature of the present invention to provide method of fabricating a microstructure that allows for the rapid construction of smooth three-dimensional microstructure geometries.
It is a still further object and feature of the present invention to provide a method of fabricating a microstructure that facilitates the speedy manufacture of such devices.
In accordance with the present invention, a method is provided for fabricating a microstructure. The method includes the steps of providing a layer of polymerizable material and bringing a solid into contact with the layer. The layer of polymerizable material is polymerized such that the layer solidifies. The solid may be disengaged from the layer after the layer is polymerized or moved during the step of polymerizing the layer. Alternatively, the solid may be dissolved after the layer is polymerized. The solid may be hydrophilic or hydrophobic. It is understood that the term xe2x80x9chydrophilicxe2x80x9d as used herein shall mean any material that has a strong affinity or preference for the polymerizable material. The term xe2x80x9chydrophobicxe2x80x9d shall mean any material that has a lack of affinity for or an aversion to the polymerizable material.
It is contemplated to position the layer in a gas such that the layer and the gas intersect at an interface that has a generally curved shape adjacent to the solid. The solid may be moved into the layer of polymerizable material prior to the step of polymerizing the layer or drawn away from the layer of polymerizable material prior to the step of polymerizing the layer so as to form the curved shape of the interface.
In accordance with the further aspect of the present invention, a method is provided of forming a microstructure. The method includes the step of providing a layer of polymerizable material having an upper surface. The upper surface of the polymerizable material has a shape, and is engaged with a solid object so as to alter the shape thereof. Thereafter, the layer is solidified by polymerization.
The solid object may be disengaged from the layer after the layer is polymerized or moved during the step of polymerizing the layer. It is contemplated to move at least a portion of the solid object into the layer prior to the step of polymerizing the layer. Thereafter, the portion of the solid object in the layer may be moved towards the upper surface of the layer prior to the step of polymerizing the layer. Alternatively, a portion of the solid object may engage the upper surface of the layer. The portion of the solid object that engages the upper surface is dissolved after the layer is polymerized.
In accordance with a further aspect of the present invention, a method of forming a microstructure is provided. The method includes the step of depositing a polymerizable material on a base layer. The polymerizable material has an interface with a fluid. The interface is manipulated with a solid object to a user desired shape. Thereafter, the polymerizable material is polymerized such that the interface retains a shape corresponding to the user desired shape.
In order to manipulate the interface, the interface is engaged by the solid object. The solid object is moved into contact with the interface, and thereafter, drawn away from the base layer. The solid object is maintained at a predetermined position while the polymerizable material is polymerized. The polymerizable material is polymerized by directing a polymerizing agent towards the polymerizable material.